How do sunscreens work?

I know I've been pretty slack with the science posts (thesis writing makes me never want to read another science article again!), but I decided to do this one, because a few people have asked me about it recently. There'll be a few sciencey DIY beauty projects soon though, hope that satisfies any nerdy cravings! :)

photo credit: mark sebastian

How do sunscreens work?

There are two main types of sunscreens: chemical and physical. Often a tube of sunscreen will contain a combination of the two.


Physical sunscreens work by blocking out, absorbing and scattering UV. They essentially work like a million little men standing on your skin holding umbrellas. Examples of physical sunscreens are zinc oxide and titanium dioxide - the "nano" sunscreens fall in this category.

Chemical sunscreens are a bit more complex. Some organic (meaning carbon-based, not pesticide-free!) chemicals can absorb UV light. The process is a bit complex to explain (it's a barrel of fish containing pi electrons and discrete energy levels), but the result is that chemicals which have a double bond/single bond/double bond structure are able to absorb UV light and dissipate it as heat energy. Examples of chemical sunscreens include oxybenzone and ensulizole - as you can see, they have lots of double/single/double bond patterns which allow them to absorb UV light.

An analogy to how this works is when black objects absorb visible light and turn it into heat energy, which is why most people don't wear black to the beach!